This invention relates to an oilless reciprocal compressor that is suitable for mounting on the inside wall of a cargo container and for carrying perishable foodstuffs such as fruits and vegetables.
Cargo containers are typically carried on the open decks of sea going vessels and are thus exposed to a harsh salt air environment. The containers are made generally air tight and the inside environment of the container is maintained at a desired temperature by self-sustaining air conditioning equipment. As many of the components as possible are brought inside the container to protect them from the harsh outside environment. This however, consumes valuable cargo space and it is therefore important to package the equipment to minimize space.
The cargo containers typically undergo rough handling, oftentimes being bumped or dropped from relatively high elevations as they are being loaded and unloaded from carriers. Accordingly, the equipment stored in the container must be securely fastened in place so that it cannot break loose thus endangering the cargo.
In the case of cargo containers used to carry perishable fruits and vegetables, it is highly desirable to replace the oxygen within the container with nitrogen gas which serves to better preserve the perishable foodstuff. To this end, systems have been derived wherein outside air is first compressed and then passes through a series of filters and membranes to separate nitrogen gas from the incoming air. The nitrogen is discharged into the container while the other separated air constituents, including oxygen, are exhausted to ambient.
Small reciprocating air compressors such as the compressor described in U.S. Pat. No. 5,244,363 to Olson possess the operating parameters that are required for use in this type of nitrogen generation system. The prior art compressors, however, have two undesirable features that make them less than attractive for use in this particular application. First, crankcase oil can move past the piston rings and find its way into the compressed air stream. This, in turn, has an adverse effect on downstream filters and separating membranes as well as the products stored in the container. Secondly, reciprocating air compressors that are presently available generally include self contained cooling fans that are space consuming. They also have relatively weak mounting brackets that cannot withstand the rough handling that a cargo container is exposed to and do not lend themselves to wall mounting because of bearing loading considerations.